Cable structures for hauling electrical power, hydraulic and electrical signal transmission lines are typically used in oil wells for the installation, operation and retrieval of electrical pumps and other apparatus attached to the down-hole end of the structure.
Prior art cable structures used for this purpose are generally flat and comprise a core of power and hauling lines surrounded by a helically-wound, interlocked armor tape. An example of a prior art cable of this type is disclosed in copending U.S. Pat. No. 4,644,094, of Ernest G Hoffman, issued Feb. 17, 1987 and in U.S. Pat. No. 4,716,260 of Ernest G. Hoffman and David H. Neuroth, issued Dec. 29,1987 both of said applications being assigned to the same assignee as the instant application.
To chemically treat bottom hole oil wells, a hollow flexible conduit, which typically takes the form of a corrugated steel tubing, is inserted into the well. This tubing serves as the medium through which an appropriate treatment fluid, such as liquid nitrogen, is able to be injected into the well. A pair of coacting vertical endless traction belts mounting laterally spaced apart cleats is typically used for driving the tubing into and pulling the tubing out of the particular bore hole. This type of meshing drive means is often referred to as an "injector" and normally has its belts oriented in vertical alignment with the surface entrance to the bore hole. The tubing is gripped tightly between the coacting cleats which translate in the vertical plane upon rotation of the traction belts or chains to impart vertical movement to the tubing. A powered reel is typically used to store, pay out and accumulate the tubing.
An injector of this type is disclosed, for example, in U.S. Pat. No. 3,285,485 which issued to Damon T. Slator on Nov. 15, 1966.
Inasmuch as a source of pushing and pulling forces is available with injectors, it would be advantageous to have a cable which could also effectively utilize these commercially-available meshing drives as a means for positively driving the cable structure and any equipment attached to the cable's down-hole end past obstructions and deviations in the bore hole.
To be able to utilize the available mesh drives effectively, the cable structure preferably should posses the feature of being able to efficiently convert the available drive forces into high magnitude axial pushing and pulling forces which can be concentrated along the longitudinal axis of the cable structure and hence, parallel to the desired direction of cable translation.
As disclosed in our aforementioned copending patent applications, an armored cable structure which is formed by overlapping and interlocked convolutions of armor windings may be compressively driven to move the cable structure in an oil well. The armor is coupled to the hauling lines through a vertebrae-like structure which efficiently transmits the longitudinal and normal components of frictional forces applied to the outer surface of the armor through the cable structure to the hauling lines.
In these cable structures the axial components of the driving forces will be substantially equal to the coefficient of friction between the surface of the armor and the drive means contacting that surface multiplied by the magnitude of the force components normal to that surface. For certain field applications, particularly deep well applications, which require that considerable lengths, and correspondingly considerable weights of cable be raised and lowered or for other field applications where considerable pushing and pulling forces are required to force the cable and its attached equipment axially past obstructions in the bore hole, it may be necessary to utilize positive meshing drives as an alternative to frictional engagement or as a supplement to frictional engagement.
Although meshing drives have been used by others in the past to drive cable structures axially in bore holes, the cable structure, in my opinion, has not been constructed to utilize this type of engagement in an optimum fashion. For example, in U.S. Pat. No. 4,374,530 to John B. Walling, there is disclosed a cable structure which is reinforced by a succession of spaced-apart striker plates. The plates are designed to be engaged by the teeth of a drive sprocket which provide a mesh drive with the cable structure. Specifically, each striker plate has a transversely grooved face for meshing with the teeth of the drive sprocket and the plates are separated along the length of the structure by intervening lengths of flexible polymeric production tubing employed to provide bendability to the structure. With this arrangement, the plates are positively and successively engaged by rotation of the drive sprocket teeth to move the cable structure longitudinally.
One disadvantage of the Walling cable structure is that the striker plates are designed simply to receive but not to grip the longitudinal tensile elements which are used to suspend the cable structure. Hence, when long lengths of cable are suspended, the weight of the suspended length of the cable hanging below the engaged striker plate may cause the tensile elements to slide through the bores in which they are received in the engaged striker plate causing undesirable separations to occur between various parts of the suspended structure. In addition, the flexible nature of the ploymeric production tubing may allow it to elongate axially during usage. Since the striker plates in Walling are maintained in their axially spaced relationship by the abutting and underlying tubing, it is apparent that the axial distance or pitch between the grooves in successive striker plates could vary, especially as the cable is withdrawn under tension from the bore hole. At this time, elongation of the intervening polymeric tubing sections can be most appreciable, as will be obvious. If the pitch of adjacent striker plates increases as a result, the sprocket teeth which remain of fixed pitch may not mesh precisely with the metal grooves in the striker plates, thus allowing slippage to occur between the sprocket teeth and the cable structure or, in severe situations, possibly allowing the sprocket teeth to engage and pinch the intervening sections of polymeric tubing and the conduits contained therein.